Medical Image Processing Device, Operation Method Therefor, and Endoscope System

1. A medical image processing device comprising: a processing circuitry configured for: performing input processing of a first color image signal; calculating a first signal ratio between image signals of two colors in the first color image signal and a second signal ratio between image signals of two colors different from those in the first signal ratio; and performing, in a feature space formed by the first signal ratio and the second signal ratio, first processing for moving, among a first range, a second range, and a third range where an observation target in a subject is distributed, the coordinates of the second range to a reference range which is a low saturation range not including the first range and the third range determined in the feature space, and second processing for moving at least one of the coordinates of the first range and the coordinates of the third range to expand a hue difference between the first range and the third range while maintaining a saturation difference with the second range; wherein coordinates within a radius vector variation range are moved to the reference range in the first processing, the radius vector variation range having a radius vector and an angle each of which is within a predetermined range in the feature space, the second range being included in the radius vector variation range, and the first range and the third range being not included in the radius vector variation range, and wherein an angle of coordinates within an angle variation range is changed while a radius vector of the coordinates of the angle variation range is not changed in the second processing, the angle variation range including at least one of the first range and the third range.

2. The medical image processing device according to claim 1 , wherein the first processing is performed for moving the coordinates of the second range to the reference range by changing a radius vector of the coordinates of the second range in the feature space.

3. The medical image processing device according to claim 1 , wherein the second processing is performed for moving the coordinates of the first range and the coordinates of the third range so as to be distant from each other by changing an angle of the coordinates of the first range and an angle of the coordinates of the third range in the feature space.

4. The medical image processing device according to claim 1 , wherein the reference range is a range which includes the origin of the feature space, and does not include the first range and the third range.

5. The medical image processing device according to claim 1 , wherein the processing circuitry is further configured for: performing, in the feature space, first processing for moving the coordinates of the second range to a reference range determined in the feature space, and in the feature space, third processing for moving the third range in a state where the coordinates of the first range are maintained.

6. The medical image processing device according to claim 5 , wherein the third processing is performed for moving the coordinates of the third range such that the hue of a second special image obtained from the first signal ratio and the second signal ratio after the first and third processing is changed.

7. The medical image processing device according to claim 5 , wherein the processing circuitry is further configured for: converting the first signal ratio and the second signal ratio after the first and second processing to a second color image signal or converts the first signal ratio and the second signal ratio after the first and third processing to a second color image signal; and adjusting the pixel values of the second color image signal from first brightness information obtained from the first color image signal and second brightness information obtained from the second color image signal.

8. The medical image processing device according to claim 1 , wherein, in the feature space, the difference between the first range and the second range in a case where the image signal of at least one color of the first color image signal is a narrowband signal is greater than the difference between the first range and the second range in a case where the image signals of all colors of the first color image signal are broadband signals, or the difference between the first range and the third range in a case where the image signal of at least one color of the first color image signal is a narrowband signal is greater than the difference between the first range and the third range in a case where the image signals of all colors of the first color image signal are broadband signals.

9. The medical image processing device according to claim 1 , wherein the first signal ratio correlates with a blood vessel depth and the second signal ratio correlates with a blood volume.

10. The medical image processing device according to claim 9 , wherein the first signal ratio is a B/G ratio and the second signal ratio is a G/R ratio.

11. An endoscope system comprising: the medical image processing device according to claim 5 ; and a display unit which displays a first special image obtained from the first signal ratio and the second signal ratio after the first and second processing and a second special image obtained from the first signal ratio and the second signal ratio after the first and third processing.

12. An operation method for a medical image processing device comprising: a step in which a processing circuitry performs input processing of a first color image signal; a step in which the processing circuitry calculates a first signal ratio between image signals of two colors in the first color image signal and a second signal ratio between image signals of two colors different from those in the first signal ratio; and a step in which the processing circuitry performs, in a feature space formed by the first signal ratio and the second signal ratio, first processing for moving, among a first range, a second range, and a third range where an observation target in a subject is distributed, the coordinates of the second range to a reference range which is a low saturation range not including the first range and the third range determined in the feature space, and second processing for moving at least one of the coordinates of the first range and the coordinates of the third range to expand a hue difference between the first range and the third range while maintaining a saturation difference with the second range; wherein coordinates within a radius vector variation range are moved to the reference range in the first processing, the radius vector variation range having a radius vector and an angle each of which is within a predetermined range in the feature space, the second range being included in the radius vector variation range, and the first range and the third range being not included in the radius vector variation range, and wherein an angle of coordinates within an angle variation range is changed while a radius vector of the coordinates of the angle variation range is not changed in the second processing, the angle variation range including at least one of the first range and the third range.